Vitamin D receptor gene Fok1 polymorphism predicts calcium absorption and bone mineral density in children

A systematic review of the association between common single nucleotide polymorphisms and 25-hydroxyvitamin D concentrations

In order to appreciate the association between hypovitaminosis D and various adverse health outcomes, we require a thorough understanding of how common single nucleotide polymorphisms (SNPs) influence serum concentrations of 25-hydroxyvitamin D (25OHD). We undertook a systematic review of the literature in order to identify studies that examined 25OHD concentrations, and common SNPs. We found nine studies related to the vitamin D binding protein (group-specific component, GC), and five studies examining the vitamin D receptor (VDR). SNPs in a range of cytochrome P450 enzymes have also been examined in seven studies. Replicated findings have been found between 25OHD concentrations and (a) two SNPs in GC (rs4588, rs7041), (b) one SNP in VDR (rs10735810), and (c) one SNP in CYP27B1 (rs10877012). In light of these associations, it is feasible that optimal concentrations of 25OHD required to reduce disease outcomes may vary according to genotype. We speculate that recently identified U-shaped relationships between 25OHD concentrations and disease outcomes (i.e. increased risk at both high and low concentrations) may reflect a mixture of genotype-defined subgroups. Further research is required in order to clarify the genetic architecture underlying 25OHD serum concentrations, and to unravel the mechanisms of action responsible for these associations.

Polymorphism in vitamin D receptor is associated with bone mineral density in patients with adolescent idiopathic scoliosis

Low bone mass and osteopenia have been reported in the axial and peripheral skeleton of adolescent idiopathic scoliosis (AIS) patients. Furthermore, several recent studies have shown that gene polymorphisms are related to osteoporosis. However, no study has yet linked polymorphisms in the vitamin D receptor (VDR) gene and bone mass in AIS. Accordingly, the authors examined the association between bone mass and VDR gene polymorphisms in 198 girls diagnosed with AIS. The VDR BsmI (rs1544410), FokI (rs2228670) and Cdx2 (rs11568820) polymorphisms and bone mineral density at the lumbar spine (LSBMD) and femoral neck (FNBMD) were analyzed and compared to their levels in healthy controls. Mean LSBMD and FNBMD in AIS patients were lower than in age- and sex-matched healthy controls (P = 0.0022 and P = 0.0013, respectively). A comparison of genotype frequencies in AIS patients and controls revealed a significant difference for the BsmI polymorphism only (P = 0.0054). Furthermore, a significant association was found between the VDR BsmI polymorphism and LSBMD. In particular, LSBMD in AIS patients with the AA genotype was found to be significantly lower than in patients with the GA (P < 0.05) or GG (P < 0.01) genotypes. However, no significant association was found between LSBMD or FNBMD and the VDR FokI or Cdx2 polymorphisms. These results suggest that the VDR BsmI polymorphism is associated with LSBMD in girls with AIS.

Effect of age, gender and calciotropic hormones on the relationship between vitamin D receptor gene polymorphisms and bone mineral density

BACKGROUND/OBJECTIVES

Hypovitaminosis D is a major public health problem worldwide and unexpectedly more so in sunny countries. Vitamin D receptor (VDR) gene is associated with inter-individual variance in bone mineral density (BMD). Studies assessing the effect of VDR gene polymorphisms on BMD yielded conflicting results. The aim of this study was to assess the relationship between VDR polymorphisms and BMD in the Lebanese, across age groups and genders and to assess the effect of PTH and lean mass and vitamin D levels on such relationship.

SUBJECTS/METHODS

In total, 203 subjects aged 65-85 years and 336 children aged 10-17 years. Polymorphisms in the VDR gene were assessed with the restriction enzymes BsmI, TaqI and ApaI. Bone mineral content, BMD and lean mass were measured using Dual-Energy X-ray Absorptiometry (DXA). The dominant hand strength was measured in children.

RESULTS

Heterozygote genotype was the most frequent in both age groups. There was no difference in the frequency distribution of genotypes between the young and the elderly. No relationship between VDR genotypes and lean mass was found in either age group. Heterozygote boys had the lowest parathormone (PTH) and heterozygote elderly women had the highest BMD at the spine and forearm.

CONCLUSIONS

In the Lebanese, the relationship between VDR polymorphisms and BMD differs by age. Survival does not seem to differ by VDR genotype. However, further studies are needed to assess the effect of VDR gene polymorphisms on mortality per se and time to mortality, not evaluated in this study.

Does vitamin D supplementation of healthy Danish Caucasian girls affect bone turnover and bone mineralization?

INTRODUCTION

A high peak bone mass may be essential for reducing the risk of osteoporosis later in life and a sufficient vitamin D level during puberty may be necessary for optimal bone accretion and obtaining a high peak bone mass. Dietary intake and synthesis during winter of vitamin D might be limited but the effect of vitamin D supplementation in adolescence on bone mass is not well established.

OBJECTIVE

To investigate the effect of supplementation with 5 and 10 microg/day vitamin D(3) for 12 months in 11- to 12-year-old girls on bone mass and bone turnover as well as the possible influence of VDR and ER genotype on the effect of the supplementation.

METHODS

The girls (n=221) were randomized to receive either 5 microg or 10 microg vitamin D(3) supplementation per day or placebo for 12 months. Whole body and lumbar spine bone mass measured by DXA and pubertal status were determined at baseline and after 12 months whereas physical activity and dietary intake of calcium and vitamin D were assessed at baseline. Serum (S) 25-hydroxyvitamin D (25OHD), S-osteocalcin, S-parathyroid hormone, S-calcium, S-inorganic phosphate, urinary (U) pyridinoline (Pyr) and deoxpyridinoline (Dpyr) were measured at baseline and after 6 and 12 months.

RESULTS

The S-25OHD concentration increased (p<0.001) relative to the baseline values in the groups receiving either 5 microg/day (mean+/-SD; 11.0+/-10.3 nmol/l, baseline 41.9+/-17.6 nmol/l) or 10 microg/day (13.3+/-11.8 nmol/l, baseline 44.4+/-16.6 nmol/l) vitamin D(3) for 12 months compared to placebo (-3.1+/-9.8 nmol/l, baseline 43.4+/-17.1 nmol/l). There was no effect of vitamin D-supplementation on biomarkers for bone turnover or on whole body or spine bone mineral augmentation. However, vitamin D supplementation increased whole body bone mineral density (BMD) (p=0.007) and bone mineral content (BMC) (p=0.048) in the FF VDR genotype but not in the Ff or ff VDR genotypes.

CONCLUSION

Supplementation with vitamin D (5 or 10 microg/day) over 12 months increased the S-25OHD concentration but there was no effect on indices of bone health in the entire group of girls. However, there was an effect on BMD for a subgroup with the FF VDR genotype indicating an influence of genotype.

Factors affecting calcium balance in Chinese adolescents

Chinese dietary reference intakes (DRIs) for calcium were developed mainly from studies conducted amongst Caucasians, yet a recent review showed that reference calcium intakes for Asians are likely to be different from those of Caucasians (Lee and Jiang, 2008). In order to develop calcium DRIs for Chinese adolescents, it is necessary to explore the characteristics and potential influencing factors of calcium metabolic balance in Chinese adolescents. A total of 80 students (15.1+/-0.8 years) were recruited stratified by gender from a 1-year calcium supplementation study. Subjects were randomly designed to four groups and supplemented with calcium carbonate tablets providing elemental calcium at 63, 354, 660, and 966 mg/day, respectively. Subjects consumed food from a 3-day cycle menu prepared by staff for 10 days. Elemental calcium in samples of foods, feces, and urine was determined in duplicates by inductively coupled plasma atomic emission spectrometry. The total calcium intake ranged from 352 to 1323 mg/day. The calcium apparent absorption efficiency and retention in boys were significantly higher than that in girls (68.7% vs. 46.4%, 480 mg/day vs. 204 mg/day, P<0.05). Calcium retention increased with calcium intakes, but did not reach a plateau. Calcium absorption efficiency in boys increased with calcium intake up to 665 mg/day, and decreased after that. In girls, calcium absorption efficiency decreased with calcium intake. Calcium absorption efficiency increased within 1 year after first spermatorrhea in boys, but decreased with pubertal development in girls. Sex, calcium intake, age, and pubertal development were the most important determinants of calcium absorption (R(2)=0.508, P<0.01) and retention (R(2)=0.745, P<0.05). This study indicates that sex, calcium intake, age, and pubertal development are important factors for calcium retention and absorption during growth, which should be considered for the development of calcium DRIs for Chinese adolescents.

Vitamin D receptor gene polymorphisms modulate the skeletal response to vitamin D supplementation in healthy girls

OBJECTIVES

Vitamin D receptor (VDR) gene plays an important role in bone mass regulation. We have previously shown a beneficial effect of vitamin D supplementation on bone mass in girls. This study investigated whether the musculo-skeletal response to Vitamin D was modulated by polymorphisms in VDR gene.

DESIGN

Randomized placebo-controlled trial.

METHODS

179 girls (10-17 years), were randomly assigned to placebo or Vitamin D3 for one year. VDR genotypes were determined in 167 girls using BsmI, TaqI and ApaI restriction enzymes. Bone mass at the spine, hip, forearm and total body, and lean mass were measured by DXA at baseline and at one year.

RESULTS

After one year, VDR gene polymorphisms using Bsm1 and TaqI restriction enzymes were associated with percent changes in bone area, BMC and BMD at multiple skeletal sites in the Vitamin D3 group but not in the placebo group. The least increments were observed in the BB and tt genotypes. No similar effect was observed with ApaI enzyme. This relationship between VDR genotypes and changes in BMD and BMC remained significant after adjustment for puberty, changes in lean mass, height and bone area.

CONCLUSION

VDR gene polymorphisms influence the skeletal response to vitamin D supplementation in healthy adolescent girls.

Higher serum 25-hydroxyvitamin D levels in school-age children are inconsistently associated with increased calcium absorption

CONTEXT

Increasing serum 25-hydroxyvitamin D (25-OHD) in adults may enhance calcium absorption (Ca-abs). There are few similar pediatric data leading to uncertainty about the optimal target for 25-OHD to maximize Ca-abs.

OBJECTIVE

Our objective was to evaluate the relationship between 25-OHD and Ca-abs in a large cohort of school-age children and adolescents.

DESIGN

We evaluated data from 439 Ca-abs measurements performed using dual-tracer stable isotope techniques conducted at our center over a 15-yr period in 251 healthy children, 4.9-16.7 yr of age.

RESULTS

Serum 25-OHD ranged from 28 to 197 nmol/liter (mean 85 +/- 2 nmol/liter) (sem). Total Ca-abs (intake times fractional absorption) were significantly correlated to 25-OHD in the whole population (r = 0.16, P = 0.001). This relationship was closer in the 197 studies in early puberty (Tanner 2 or 3, r = 0.35, P < 0.001) and not significant in pre- or late pubertal subjects. For the whole population, fractional Ca-abs adjusted for calcium intake were slightly but significantly higher at 25-OHD of 28-50 nmol/liter (0.344 +/- 0.019) compared with 25-OHD of 50-80 nmol/liter (0.280 +/- 0.014) or 25-OHD greater than 80 nmol/liter (0.297 +/- 0.015, P < 0.01 for each), suggesting adaptation to moderately low 25-OHD values.

CONCLUSION

There is no consistent pattern of relationship between 25-OHD and either fractional or total calcium absorption in school-age children. However, there appears to be a modest calcium absorptive response to higher 25-OHD during early puberty.

Update on the pharmacogenetics of the vitamin D receptor and osteoporosis

Vitamin D and calcium are essential for normal skeletal growth and for maintaining the mechanical and structural integrity of the skeleton. Reduced intake of calcium and vitamin D may be associated with reduced bone mass and osteoporosis while a chronic and severe vitamin D deficiency may lead to osteomalacia. Given the importance of vitamin D in bone homeostasis, common polymorphisms in the vitamin D receptor gene were the first to be investigated as possible determinants of bone mass and fracture risk. Even though results are still conflicting and the molecular mechanisms by which these polymorphisms influence receptor activity remain in part to be investigated, an additional important issue is represented by their potential pharmacogenomic and pharmacogenetic implications. This review analyzes major pharmacogenetic studies of polymorphisms in the vitamin D receptor gene and osteoporosis.

The vitamin D receptor Fok1 polymorphism and bone mineral density in Chinese children

BACKGROUND

To evaluate the relationship between vitamin D receptor (VDR) gene polymorphism and bone mineral density (BMD) in 213 healthy children aged 6-10 year in China.

METHODS

A questionnaire survey of dietary pattern, outdoor activity was conducted among 213 children (boys 126, girls 86) randomly selected in Xishui county of Hubei province. The BMD was determined by dual energy X-ray absorptiometry at the distal forearm, calcium, phosphorus, and alkaline phosphatase in serum were immediately analyzed. The FokI polymorphism was detected by using PCR-RFLP.

RESULTS

BMD was significantly higher in boys than in girls in 8/9 year group. (2) the frequencies of FF, Ff, and ff genotype were 25.8%, 62.0% and 12.2%, respectively; no difference was found between boys and girls. (3) BMD of children carrying FF genotype was higher (0.256+/-0.03) than those of carrying Ff genotype (0.241+/-0.03), P<0.01; the Ff genotype was associated with lowest forearm BMD in both boys and girls. Outdoor activity also positively affected peak bone mass.

CONCLUSION

The Fok1 polymorphism of the VDR receptor seems to directly affect bone mineral mass in Chinese children.

Rickets in the Middle East: role of environment and genetic predisposition

CONTEXT

The Middle East has a high incidence of rickets, and it is also common in Europe-dwelling children of Middle Eastern origin.

OBJECTIVE

The objective of the study was to explore the mechanisms leading to rickets in children of the Middle East.

DESIGN AND SETTING

We conducted a prospective study in 98 rachitic and 50 controls (aged 6 months to 4 yr) from university and community outpatient hospitals in Egypt and Turkey.

MAIN OUTCOME MEASURES

We collected epidemiological, maternal, nutritional, radiographic, and biochemical parameters; markers of bone turnover; and vitamin D receptor (VDR) gene polymorphisms.

RESULTS

Epidemiological factors had a key role in pursuit of rickets; Egyptian and Turkish patients had lower (P < 0.01) dietary calcium intake than controls and the recommended dietary intakes, and serum 25-hydroxyvitamin D levels were reduced in patients, the difference with controls being significant (P < 0.001) only in Turkey, although rickets was more severe in Egypt as determined by the x-ray score (P < 0.05). In Turkey, the F VDR allele frequency was significantly (P < 0.05) increased in patients. The BB VDR genotype was associated with lower serum 25-hydroxyvitamin D levels in both patients and controls and with severity of rickets.

CONCLUSIONS

In Turkey most patients had vitamin D deficiency, whereas in Egypt they had mostly calcium insufficiency combined with vitamin D deficiency. In this environ, VDR genotypes may predispose to rickets by increased frequency of the F allele. The unique environs and genetic predisposition have to be accounted for in the design of preventive measures, rather than using European or American recommended dietary intake for calcium and vitamin D.

The health benefits of calcium citrate malate: a review of the supporting science

There has been considerable investigation into the health benefits of calcium citrate malate (CCM) since it was first patented in the late 1980s. This chapter is a comprehensive summary of the supporting science and available evidence on the bioavailability and health benefits of consuming CCM. It highlights the important roles that CCM can play during various life stages. CCM has been shown to facilitate calcium retention and bone accrual in children and adolescents. In adults, it effectively promotes the consolidation and maintenance of bone mass. In conjunction with vitamin D, CCM also decreases bone fracture risk in the elderly, slows the rate of bone loss in old age, and is of benefit to the health and well-being of postmenopausal women. CCM is exceptional in that it confers many unique benefits that go beyond bone health. Unlike other calcium sources that necessitate supplementation be in conjunction with a meal to ensure an appreciable benefit is derived, CCM can be consumed with or without food and delivers a significant nutritional benefit to individuals of all ages. The chemistry of CCM makes it a particularly beneficial calcium source for individuals with hypochlorydia or achlorydia, which generally includes the elderly and those on medications that decrease gastric acid secretion. CCM is also recognized as a calcium source that does not increase the risk of kidney stones, and in fact it protects against stone-forming potential. The versatile nature of CCM makes it a convenient and practical calcium salt for use in moist foods and beverages. The major factor that may preclude selection of CCM as a preferred calcium source is the higher cost compared to other sources of calcium commonly used for fortification (e.g., calcium carbonate and tricalcium phosphate). However, formation of CCM directly within beverages or other fluid foods and/or preparations, and the addition of a concentrated CCM solution or slurry, are relatively cost-effective methods by which CCM can be incorporated into finished food and beverage products.

Association of the VDR translation start site polymorphism and fracture risk in older women

We evaluated the association between the VDR translation start site polymorphism and osteoporotic phenotypes among 6698 older white women. Women with the C/C genotype had lower wrist BMD and an increased risk of wrist and all non-spine/low-trauma fractures. The high frequency of this variant confers a population attributable risk that is similar to several established risk factors for fracture.

INTRODUCTION

The vitamin D receptor (VDR) is a nuclear receptor that regulates bone formation, bone resorption, and calcium homeostasis. A common C to T polymorphism in exon 2 of the VDR gene introduces a new translation start site and a protein that differs in length by three amino acids (T = 427aa, C = 424aa; rs10735810).

MATERIALS AND METHODS

We conducted genetic association analyses of this polymorphism, BMD, and fracture outcomes in a prospective cohort of 6698 white American women >or=65 years of age. Incident fractures were confirmed by physician adjudication of radiology reports. There were 2532 incident nontraumatic/nonvertebral fractures during 13.6 yr of follow-up including 509 wrist and 703 hip fractures.

RESULTS

Women with the C/C genotype had somewhat lower distal radius BMD compared with those with the T/T genotype (CC=0.358 g/cm(2), CT=0.361 g/cm(2), TT=0.369 g/cm(2), p=0.003). The C/C genotype was also associated with increased risk of non-spine, low traumatic fractures (HR: 1.18; 95% CI: 1.04, 1.33) and wrist fractures (HR: 1.33; 95% CI: 1.01, 1.75) compared with the T/T genotype in age-adjusted models. Further adjustments for distal radius BMD only slightly attenuated these associations. The VDR polymorphism was not associated with hip fracture. The population attributable risk (PAR) of the C/C genotype for incident fractures was 6.1%. The PAR for established risk factors for fracture were: low femoral neck BMD (PAR=16.3%), maternal history of fracture (PAR=5.1%), low body weight (PAR=5.3%), corticosteroid use (PAR=1.3%), and smoking (PAR=1.6%). Similar PAR results were observed for wrist fractures.

CONCLUSIONS

The common and potentially functional VDR translation start site polymorphism confers a modestly increased relative risk of fracture among older white women. However, the high frequency of this variant confers a population attributable risk that is similar to or greater than several established risk factors for fracture.

Steroid hormone receptor gene polymorphisms and osteoporosis: a pharmacogenomic review

Osteoporosis is a common skeletal disorder with a strong genetic component. In recent years, significant progress has been made in understanding the genetic basis of osteoporosis. Given the biological significance of signalling through steroid hormone receptors, bone biology and calcium homeostasis, alleles of steroid hormone receptor genes have been postulated to contribute to the well-documented genetic predisposition to osteoporosis; and in different studies, these alleles have been associated with variation in bone mass and fracture risk. Even though results are still conflicting and the molecular mechanisms by which these polymorphisms influence receptor activity remain, in part, to be investigated, an additional important issue is represented by potential pharmacogenomic (the investigation of variations of DNA or RNA characteristics as related to drug response) or pharmacogenetic (the influence of variations of DNA sequence on drug response) implications. In fact, steroid hormone receptors actually mediate the action of several compounds known to positively or negatively affect bone homeostasis, such as vitamin D, estrogen and glucocorticoids. This review analyses major pharmacogenetic studies of polymorphisms in steroid hormone receptor genes.

Impact of genetic variation on metabolic response of bone to diet

There is compelling evidence to suggest that both the development of bone to peak bone mass at maturity and subsequent loss depend on the interaction between genetic, hormonal, environmental and nutritional factors. The major part (≤80%) of the age-specific variation in bone turnover and bone density is genetically determined. However, the notion of genetic determinant is of little value unless the specific genes that are involved can be identified. Most work in this area of osteoporosis research has focused on the candidate gene approach, which has identified several candidate genes for osteoporosis, including genes encoding the vitamin D receptor (VDR), oestrogen receptors (α and β), apolipoprotein E, collagen type I α 1 and methylenetetrahydrofolate reductase, amongst many others. However, in general, findings from numerous studies of the association between such genes and various bone variables have been inconsistent. In addition to possible gene—gene interactions it is likely that there are interactions between these genes and certain environmental factors, especially nutrition, that may mediate expression of bone-related phenotypes. While these potential interactions add a level of complexity to our understanding of these apparent genetic effects on bone, identification of a role for genetic factors without knowledge of their interaction with nutrients can do little to advance prevention and treatment of osteoporosis. This information is especially important because, unlike genotype, diet and nutrition can be modified. The aim of the present review is to critically evaluate current knowledge relating to candidate genes for osteoporosis, with particular emphasis on their interaction with nutrients and dietary factors in determining bone health.

A genetic approach to fracture epidemiology in childhood

The purpose of this report is to provide a review of both childhood fracture epidemiology and known heritable causes for fracture predisposition to the Medical Geneticist, who is frequently consulted to assess children with multiple or unexplained fractures for a physiologic etiology. A detailed knowledge of the clinical and laboratory evaluation for osteogenesis imperfecta (OI) and other single-gene disorders is obviously essential to complete a useful evaluation of such children. The experienced clinician will immediately recognize that single gene disorders represent only a small fraction of these patients. In infants, non-accidental trauma (NAT) unfortunately is the likely explanation for the fracture pattern, but in some infants, and certainly in older children with recurrent fractures, no medical explanations can be found. Recent studies in which bone mineral density (BMD) has been associated with genetic variation at a number of candidate genes are promising but these studies are too premature yet to be used clinically. Nonetheless, we do expect that in the future whole-genome approaches in conjunction with key clinical and epidemiological variables may be combined through an informatics approach to create better predictors of fracture susceptibility for these populations of patients.

Fractional calcium absorption is increased in girls with Rett syndrome

BACKGROUND

Rett syndrome (RTT), an X-linked neurodevelopmental disorder primarilyaffecting girls, is characterized in part by osteopenia and increased risk of skeletal fractures. We hypothesized that decreased intestinal calcium (Ca) absorption relative to dietary Ca intake and increased renal Ca excretion might cause these problems in RTT.

OBJECTIVE

We measured fractional Ca absorption, urinary Ca loss, dietary Ca intake, and the hormonal factors regulating Ca metabolism to determine whether abnormalities in Ca balance might relate to poor bone mineralization in RTT girls and to evaluate the contribution of these factors to the overall dietary Ca needs of RTT girls.

STUDY DESIGN

Ten RTT girls and 10 controls, matched for age, sex, and pubertal status, were given a 3 day constant Ca diet that mimicked their habitual intakes. At the end of each dietary period, girls received single doses of Ca (intravenous) and Ca (oral). Fractional urinary excretion of Ca, Ca, 24 hour urinary Ca, and urinary cortisol excretion were determined. Serum Ca, phosphorous, alkaline phosphatase, vitamin D metabolites, parathyroid hormone (PTH), and osteocalcin were measured in the postabsorptive state. Bone mineral content (BMC) was measured by dual-energy x-ray absorptiometry.

RESULTS

Fractional Ca absorption was significantly higher in RTT than in control girls (mean +/- SDp, 52 vs. 33 +/- 13%). Dietary Ca intake (mean +/- SDp, 1,100 vs. 1,446 +/- 440 g/d) and net Ca absorption (mean +/- SDp, 513 vs. 362 +/- 306 mg/d) did not differ significantly between RTT and controls, respectively. Although urinary Ca excretion did not differ between groups, the increased urinary Ca:creatinine ratio (mean +/- SDp, 0.39 vs. 0.23 +/- 0.38) was consistent with clinical hypercalcuria and paralleled the significantly increased urinary cortisol excretion (mean +/- SDp, 3.1 vs. 1.7 +/- 1.1 mg/kg lean body mass per day) in the RTT girls. BMC was significantly lower in RTT than in controls (mean +/- SDp, 527 vs. 860 +/- 275 g). Serum Ca, P, alkaline phosphatase, vitamin D metabolites, PTH, and osteocalcin concentrations did not differ between the groups.

CONCLUSION

Fractional Ca absorption showed a compensatory increase in the presence of adequate dietary Ca intakes, mild hypercalcuria, and pronounced bone mineral deficits in RTT girls. Whether supplemental dietary Ca could enhance fractional Ca absorption and improve bone mineralization in RTT girls is unknown.

Vitamin D receptor gene polymorphisms are linked to and associated with adult height

BACKGROUND

The vitamin D receptor (VDR) gene is important to human stature, as it mediates metabolic pathways, calcium homeostasis, and phosphate homeostasis, which influence growth.

METHODS

We examined the relationship between VDR and adult height in 1873 white subjects from 406 nuclear families. Four SNPs, namely -4817A/G at intron 1, FokI C/T at exon 2 start codon, BsmI A/G at intron 8, and TaqI T/C at exon 9 in VDR were tested for linkage and association with adult height variation by the program QTDT (quantitative transmission disequilibrium test). The bT haplotype of the BsmI and TaqI loci was further tested for its association with height in unrelated samples randomly chosen from the 406 nuclear families by traditional population association methods.

RESULTS

All four tested SNPs were linked to adult height. Within family associations with height were detected at BsmI and TaqI loci (p = 0.048 and 0.039, respectively). Analyses based on BsmI/TaqI haplotypes also revealed evidence for linkage (p = 0.05) and association (p = 0.001) with height. The bT haplotype was significantly associated with higher adult height (p = 0.033, within family association test). Such an association might be female specific and influenced by menstrual status.

CONCLUSIONS

Our results strongly suggest that VDR may be linked to and associated with adult height variation in white populations.

Vitamin D and estrogen receptor-alpha genotype and indices of bone mass and bone turnover in Danish girls

Peak bone mass is a major determinant of osteoporosis risk in later life. It is under strong genetic control; however, little is known about the identity of the genes involved. In the present study, we investigated the relationship between polymorphisms in the genes encoding the vitamin D receptor (VDR) (FokI, TaqI) and estrogen receptor-alpha (ERalpha) (PvuII, XbaI), and bone mineral density (BMD), bone mineral content (BMC), and markers of bone turnover in 224 Danish girls aged 11-12 years. BMD and BMC were measured by dual-energy X-ray absorptiometry. Serum osteocalcin, 25(OH)D, and parathyroid hormone (PTH) were measured by ELISA assays and urinary pyridinium cross-links by HPLC. Physical activity, dietary calcium, and Tanner stage were assessed by questionnaire. In general, there were no significant differences in anthropometrical variables, physical activity, dietary calcium, serum 25(OH)D, or PTH among genotype groups. BMD or BMC of lumbar spine or whole body (adjusted for body and bone size and pubertal status) were not associated with VDR or ERalpha genotypes or the combination of these genotypes. This lack of association remained even after adjustment for dietary and environmental factors. VDR genotypes had no effect on bone turnover markers. XX and PP ERalpha genotypes were associated (P < 0.05) with reduced levels of urinary pyridinium cross-links, whereas serum osteocalcin was similar among genotypes. These findings suggest that the rate of bone resorption was influenced by ERalpha genotypes, even though these biochemical differences were not evident in bone mass indices.

Two single-nucleotide polymorphisms in the human vitamin D receptor promoter change protein–DNA complex formation and are associated with height and vitamin D status in adolescent girls

Numerous association studies have dealt with single-nucleotide polymorphisms (SNPs) in coding and intronic regions of the human vitamin D receptor (hVDR) gene. We have hypothesized that phenotypic traits may also be associated with variations in VDR expression due to the presence of SNPs in promoter regions. In this work, we have studied two SNPs located 1521 bp (G/C) and 1012 bp (A/G) upstream of the transcriptional start site of the main human VDR gene promoter. One base-change in any of the two variant sites led to a dramatic change in protein-DNA complex formation using nuclear extracts from HEK293, Caco-2 and COS-7 cells. Genetic analysis of 185 healthy adolescent girls evidenced two major haplotypes: 1521G/1012A and 1521C/1012G and three main genotypes: homozygous for 1521G/1012A (21.1%), homozygous for 1521C/1012G (17.3%) and heterozygous 1521CG/1012GA (57.3%). On the basis of transfection data, promoter activity was nearly 2-fold higher with the 1521G/1012A haplotype, when compared with the 1521C/1012G haplotype. Clinical and biological association study in the adolescent cohort showed that girls with a CC/GG genotype had (i) lower circulating levels of 25-dihydroxyvitamin D, with no detectable consequence on calcium metabolism, (ii) lower serum IGF-1 levels and (iii) smaller height from 11 years of age up to adult height.

The vitamin D receptor fokI start codon polymorphism and bone mineral density in male hypogonadotrophic hypogonadism

The genetic factors determining bone mineral density (BMD) are not well characterized. Many studies have investigated the relationship between the fokI polymorphism of vitamin D receptor (VDR) gene in diverse populations and gender, resulting in conflicting outcomes. Because peak bone mass in men is closely related to sufficient androgen release, the contribution of VDR gene on BMD might have been masked by hormonal status of adulthood. We therefore investigated the relationship between the fokI polymorphism of VDR and BMD in male patients with idiopathic hypogonadotrophic hypogonadism (IHH). Sixty-five untreated male patients with IHH and 39 healthy matched controls were evaluated. fokI polymorphism ("f" allele) was detected by polymerase chain reaction (PCR)-restriction fragment length polymorphism using restriction endonuclease fokI, and BMD was measured by dual Energy X-ray absorpsiometry in lumbar spine, femur and radius. The distribution of FF, Ff, and ff alleles in patients with IHH and controls were not different (patients; 46%, 51%, 3% and controls; 51.3%, 46.1%, 2.6%, respectively). BMD levels in patients with IHH were significantly lower than controls. We categorized patients and control subjects in subgroups according to whether they had homozygous FF and heterozygous Ff genotype. No differences in BMD were seen between control subgroups, but total femur and femoral neck BMD were significantly lower in patients bearing heterozygous Ff genotype with IHH than homozygous FF ones (p=0.017 and p=0.009, respectively). Ff genotype might run down the BMD in cortical bone of femur, which needs to be proved in further studies.

Methodological considerations in measuring human calcium absorption: relevance to study the effects of inulin-type fructans

During the last 50 years, a variety of methods have been developed to estimate Ca absorption in man. Mass balances were initially used, but these were unable to accurately measure fractional Ca absorption because they cannot distinguish unabsorbed dietary Ca from endogenous faecal Ca excretion (excretion of previously absorbed Ca back into the gut). A number of isotopic methods have been developed that can measure true fractional Ca absorption, employing radioisotopes, stable isotopes, or both. Different methods involve collection of urine, faecal or plasma samples. Of the currently available methods, the dual isotope tracer method with a timed urine collection is probably the most precise and reliable. It is also relatively straightforward to carry out and avoids the need for a faecal collection. The purpose of the present paper is to discuss the general advantages and disadvantages of the different methods of Ca absorption. In addition, the limitations the different methods have in examining the possible effects of non-digestible oligosaccharides on Ca absorption will be discussed.

A combination of prebiotic short- and long-chain inulin-type fructans enhances calcium absorption and bone mineralization in young adolescents

BACKGROUND

Short-term studies in adolescents have generally shown an enhancement of calcium absorption by inulin-type fructans (prebiotics). Results have been inconsistent; however, and no studies have been conducted to determine whether this effect persists with long-term use.

OBJECTIVE

The objective was to assess the effects on calcium absorption and bone mineral accretion after 8 wk and 1 y of supplementation with an inulin-type fructan.

DESIGN

Pubertal adolescents were randomly assigned to receive 8 g/d of a mixed short and long degree of polymerization inulin-type fructan product (fructan group) or maltodextrin placebo (control group). Bone mineral content and bone mineral density were measured before randomization and after 1 y. Calcium absorption was measured with the use of stable isotopes at baseline and 8 wk and 1 y after supplementation. Polymorphisms of the Fok1 vitamin D receptor gene were determined.

RESULTS

Calcium absorption was significantly greater in the fructan group than in the control group at 8 wk (difference: 8.5 +/- 1.6%; P < 0.001) and at 1 y (difference: 5.9 +/- 2.8%; P = 0.04). An interaction with Fok1 genotype was present such that subjects with an ff genotype had the least initial response to fructan. After 1 y, the fructan group had a greater increment in both whole-body bone mineral content (difference: 35 +/- 16 g; P = 0.03) and whole-body bone mineral density (difference: 0.015 +/- 0.004 g/cm(2); P = 0.01) than did the control group.

CONCLUSION

Daily consumption of a combination of prebiotic short- and long-chain inulin-type fructans significantly increases calcium absorption and enhances bone mineralization during pubertal growth. Effects of dietary factors on calcium absorption may be modulated by genetic factors, including specific vitamin D receptor gene polymorphisms.

Vitamin D receptor genotypes influence the success of calcitriol therapy for recurrent vertebral fracture in osteoporosis

Osteoporosis is a complex multi-factorial disease where environment, diet and genetics play a role in determining susceptibility. Patients with existing vertebral fracture have a heightened risk of further recurrent vertebral fracture. The efficacy of new osteoporosis therapies is often compared to calcium supplementation. 1,25-dihydroxyvitamin D3 (calcitriol) acts through the vitamin D receptor (VDR) and is effective at reducing recurrent vertebral fracture risk. Because the VDR controls calcium metabolism, we hypothesized that genetic variation at the VDR locus may influence response to both calcium and calcitriol therapy. Postmenopausal women with osteoporosis from a 3-year study comparing calcitriol versus calcium for prevention of vertebral fractures were genotyped for VDR alleles detected by FokI, BsmI, ApaI and TaqI. Data were analysed by hierarchical log-linear analysis and robust analysis of variance for relationships to fracture outcomes. Significant differences in the vertebral fracture rate in response to calcium therapy were observed between VDR genotypes (P<0.001). Calcium appeared to be equally effective as calcitriol in particular genotypes. The response to calcitriol therapy was most pronounced in patients carrying the TaqI t allele in combination with the FokI f initiation codon variant: f+t+ carriers were 11.3-fold less likely to sustain recurrent vertebral fracture in the last 2 years of the trial while on calcitriol therapy compared to calcium (P=1.4x10(-5)). Response to both calcium and calcitriol therapy is dependent on genetic variation at the VDR locus and two loci in the VDR gene may contribute to this effect.

Vitamin D receptorFokIgenotype influences bone mineral density response to strength training, but not aerobic training

To determine the influence of the vitamin D receptor (VDR) gene FokI and BsmI genotype on bone mineral density response to two exercise training modalities, 206 healthy men and women (50-81 years old) were studied before and after approximately 5-6 months of either aerobic exercise training (AT) or strength training (ST). A totla of 123 subjects completed AT (51 men, 72 women) and 83 subjects completed ST (40 men, 43 women). DNA was extracted from blood samples of all subjects and genotyping was performed at the VDR FokI and BsmI locus to determine its association to training response. Total body, greater trochanter and femoral neck bone mineral density (BMD) were measured before and after both training programmes using dual-energy X-ray absorptiometry. VDR BsmI genotype was not significantly related to BMD at baseline or after ST or AT. However, VDR FokI genotype was significantly related to ST- but not AT-induced changes in femoral neck BMD (P < 0.05). The heterozygotes (Ff) in the ST group approached a significantly greater increase in femoral neck BMD (P = 0.058) compared to f homozygotes. There were no significant genotype relationships in the AT group. These data indicate that VDR FokI genotype may influence femoral neck BMD response to ST, but not AT.

Vitamin D receptor Fok1 polymorphisms affect calcium absorption, kinetics, and bone mineralization rates during puberty

Few studies of the VDR polymorphisms have looked at calcium metabolism or long-term effects. We measured bone mineralization and calcium metabolic parameters longitudinally in a group of 99 adolescents. We found a significant relationship between calcium absorption and skeletal calcium accretion and the Fok1, but not other VDR or related, genetic polymorphisms. It seems that the Fok1 polymorphism directly affects bone mineralization during pubertal growth through an effect on calcium absorption.

INTRODUCTION

There are few data regarding the relationship between genetic markers for low bone mass and changes in calcium metabolism in childhood or adolescence. We sought to identify the effects of polymorphisms of the vitamin D receptor (VDR) on calcium and bone mineral metabolism in a longitudinal study of pubertal adolescents.

MATERIALS AND METHODS

Adolescents (n = 99) received comprehensive stable isotope studies of calcium absorption, bone calcium kinetics, and bone mineralization. Studies were repeated 12 months later. Polymorphisms of putative genetic markers were determined and related to bone mineralization and calcium metabolic finding. Results were analyzed by ANOVA in which changes over time were determined using the initial value as a covariate.

RESULTS

Polymorphisms of the Fok1 gene of the VDR were significantly related to calcium absorption (p = 0.008) and whole body BMC (p = 0.03) and BMD (p = 0.006). The Fok1 effect on whole body BMD was significant for those with Ca intake >800 mg/day (p < 0.001), whereas for those with Ca intake < or = 800 mg/day, the Fok1 genotype did not have a significant effect on whole body BMD (p = 0.40). The Fok1 genotype was significantly related to the changes during the year in whole body calcium accretion, with the ff genotype having a 63 +/- 20 mg/day deficit compared with the FF genotype (p = 0.008).

CONCLUSIONS

The Fok1 polymorphism of the VDR receptor seems to directly affect bone mineral accretion during pubertal growth through an effect on calcium absorption. The relationship between different genetic polymorphisms and bone mineral metabolism may vary by life stage as well as diet.

Genetic association of vitamin D receptor polymorphisms with autoimmune hepatitis and primary biliary cirrhosis in the Chinese

BACKGROUND

Autoimmune hepatitis (AIH) and primary biliary cirrhosis (PBC) are two autoimmune diseases of unknown etiology. Genetic factors appear to be involved in the pathogenesis of both diseases. Vitamin D has been shown to exert multiple immunomodulatory effects, which acts through its own receptor (VDR). Polymorphisms of VDR had been implicated in several autoimmune diseases. In the present study, the association between Chinese patients with AIH, PBC and the polymorphisms in exon 2, intron 8 and exon 9 of vitamin D receptor genes was studied.

METHODS

Four candidate gene loci were investigated in 49 patients with AIH, 58 patients with PBC, and 160 healthy controls. The VDR polymorphisms were assessed by FokI, BsmI, ApaI, and TaqI endonuclease digestion after specific polymerase chain reaction (PCR) amplification.

RESULTS

The result show a significant difference in FokI polymorphism between AIH patients and controls (chi(2) = 5.47, P = 0.019), and a significant association in BsmI polymorphisms between PBC patients and controls (chi(2) = 6.52, P = 0.01). Furthermore the distribution of FokI, BsmI, ApaI, and TaqI gene types differed between Chinese healthy controls and Caucasian healthy controls.

CONCLUSION

It is suggested that there is a genetic link of VDR polymorphisms to autoimmune liver diseases such as AIH and PBC in Chinese patients. Further studies are needed to elucidate the mechanisms by which VDR polymorphisms contribute to the lose of immune tolerance in autoimmune diseases.

Association of bone mineral density with vitamin D and estrogen receptor gene polymorphisms during GnRH agonist treatment

AIMS

This study examined whether or not a decrease in bone mineral density (BMD) induced by the use of gonadotropin-releasing hormone agonist (GnRHa) during sexual maturation is affected by vitamin D receptor and/or estrogen receptor gene polymorphisms, like the phenomenon observed during the postmenopausal period.

METHODS

In 43 patients who received GnRHa therapy for 6 months to treat uterine myoma or endometriosis at our department and who were confirmed to have pituitary down-regulation, we measured bone density before and after GnRHa treatment using DXA and analyzed the bone metabolism turnover using bone metabolic markers. Polymorphisms were analyzed by RFLP using FokI and TaqI for the vitamin D receptor gene and PvuII and XbaI for the estrogen receptor gene. The then determined gene polymorphism was analyzed in relation to the percentage decreases in BMD following GnRHa treatment.

RESULTS

The patients were divided by f, t into two groups: (f, t) < 2 (Group V-I) and (f, t) > or = 2 (Group V-II). They were also divided by P, x into two groups (P, x) < 3 (Group E-I) and (P, x) > or = 3 (Group E-II). The BMD change was significantly higher in Group V-II than in Group V-I. Group E-II tended to have a higher BMD change than Group E-I, although this difference was not statistically significant.

CONCLUSION

Patients who often have f and t polymorphism are more likely to show BMD reduction following GnRHa therapy, like the phenomenon seen during the postmenopausal period, than patients with other gene polymorphisms. Measures to avoid BMD reduction are required when using GnRHa in such patients.

The effect of a high-protein, high-sodium diet on calcium and bone metabolism in postmenopausal women and its interaction with vitamin D receptor genotype

The influence of a high-Na, high-protein (calciuric) diet on Ca and bone metabolism was investigated in postmenopausal women (aged 50-67 years) who were stratified by vitamin D receptor (VDR) genotype. In a crossover trial, twenty-four women were randomly assigned to a diet high in protein (90 g/d) and Na (180 mmol/d) or a diet adequate in protein (70 g/d) and low in Na (65 mmol/d) for 4 weeks, followed by crossover to the alternative dietary regimen for a further 4 weeks. Dietary Ca intake was maintained at usual intakes (about 20 mmol (800 mg)/d). Urinary Na, K, Ca, N and type I collagen cross-linked N-telopeptide (NTx; a marker of bone resorption), plasma parathyroid hormone (PTH), serum 25-hydroxycholecalciferol (25(OH)D3), 1,25-dihydroxycholecalciferol (1,25(OH)2D3), osteocalcin and bone-specific alkaline phosphatase (B-Alkphase) were measured in 24 h urine samples and fasting blood samples collected at the end of each dietary period. The calciuric diet significantly (P<0.05) increased mean urinary Na, N, K, Ca and NTx (by 19 %) compared with the basal diet, but had no effect on circulating 25(OH)D3, 1,25(OH)2D3, PTH, osteocalcin or B-Alkphase in the total group (n 24). There were no differences in serum markers or urinary minerals between the basal and calciuric diet in either VDR genotype groups. While the calciuric diet significantly increased urinary NTx (by 25.6 %, P<0.01) in the f+ VDR group (n 10; carrying one or more (f) Fok I alleles), it had no effect in the f- VDR group (n 14; not carrying any Fok I alleles). It is concluded that the Na- and protein-induced urinary Ca loss is compensated for by increased bone resorption and that this response may be influenced by VDR genotype.

Human nutrition and food research: opportunities and challenges in the post-genomic era

Sequencing of the human genome has opened the door to the most exciting new era for nutritional science. It is now possible to study the underlying mechanisms for diet-health relationships, and in the near future dietary advice (and possibly tailored food products) for promoting optimal health could be provided on an individual basis, in relation to genotype and lifestyle. The role of food in human evolution is briefly reviewed, from palaeolithic times to modern-day hunter-gatherer societies. The aetiology of 'diseases of modern civilization', such as diabetes, heart disease and cancer, and the effect of changes in dietary patterns are discussed. The risk of disease is often associated with common single nucleotide polymorphisms, but the effect is dependent on dietary intake and nutritional status, and is often more apparent in intervention studies employing a metabolic challenge. To understand the link between diet and health, nutritional research must cover a broad range of areas, from molecular to whole body studies, and is an excellent example of integrative biology, requiring a systems biology approach. The annual cost to the National Health Service of diet-related diseases is estimated to be in excess of 15 billion, and although diet is a key component of any preventative strategy, it is not given the prominence it deserves. For example, less than 1% of the pound 1.6 billion budget for coronary heart disease is spent on prevention. The polygenic and multifactorial nature of chronic diseases requires substantial resources but the potential rewards, in terms of quality of life and economics, are enormous. It is timely therefore to consider investing in a long-term coordinated national programme for nutrition research, combining nutritional genomics with established approaches, to improve the health of individuals and of the nation.

Racial differences in the effect of early milk consumption on peak and postmenopausal bone mineral density

Studies of the effect of milk consumption on bone density have focused on white women. The applicability to other races is unclear. This study of 4316 women found a racial difference in the effect of early milk consumption on bone. Further study is required to evaluate the etiology of this difference.

INTRODUCTION

Early milk consumption has been found to influence bone mineral density positively throughout life. Previous studies leading to this finding focused on white women; there are no data to support the view that black women also gain an equivalent benefit from early milk consumption.

MATERIALS AND METHODS

Using data from the Third National Health and Nutrition Examination Survey (NHANES III), we analyzed the relationship between reported childhood and teenage milk consumption and current hip bone mineral density at four sites (femoral neck, trochanter, intertrochanter, and total hip) among postmenopausal and 20- to 39-year-old non-Hispanic white (NHW) and black (NHB) women. Potential confounding variables were accounted for in the analysis.

RESULTS

Controlling for age and body mass index, teenage milk consumption was significantly associated with higher bone mineral density at all four sites among both postmenopausal and 20- to 39-year-old white women, but was not associated with bone mineral density at any site among black women. A similar pattern was observed for childhood milk intake. The interaction between race and teenage milk consumption significantly explained postmenopausal bone mineral density at all sites, whereas the interaction between race and teenage milk consumption was significant at two of the four sites among the 20- to 39-year-old women.

CONCLUSION

The results show racial differences in the effect of early milk consumption on peak and postmenopausal bone mineral density.

Vitamin D receptor gene polymorphism is associated with chronic periodontitis

Chronic periodontitis (CP) is caused by enhanced resorption of the alveolar bone supporting the teeth and is associated with intraoral inflammation after infection with certain bacteria. The VDR gene polymorphism was reported recently to be deeply related to the occurrence of tuberculosis and infection of chronic hepatitis B virus. This may be interpreted to indicate a close relationship between VDR gene polymorphism and the immunological action, because vitamin D activates monocytes, stimulates cell-mediated immunity, and suppresses lymphocyte proliferation. The purpose of the present study was to clarify whether polymorphisms in VDR gene exons are associated with the incidence of CP. A case-controlled study was performed on a group of 168 unrelated Japanese subjects whose ages ranged from 35 to 65 years. The Taq I polymorphism in the VDR gene was found to be associated significantly with CP (X2=4.48, P=0.034). We performed multiple logistic regression analyses on the TT genotype, which was found to be associated with CP, and on well-recognized risk factors, smoking and diabetes. The odds ratio (OR) for the genotype (TT/Tt) was 2.73 (95% CI 1.11-6.68, P=0.028), being larger than the unadjusted value. This indicates that the VDR gene polymorphism (TT genotype) is a risk factor for CP, independently of smoking and diabetes.

Association of polymorphisms of interleukin-6, osteocalcin, and vitamin D receptor genes, alone or in combination, with bone mineral density in community-dwelling Japanese women and men

We examined whether the -634C-->G, 298C-->T, and 2C-->T polymorphisms of the IL-6, osteocalcin, and vitamin D receptor (VDR) genes, respectively, were associated, alone or in combination, with bone mineral density (BMD) in community-dwelling Japanese women (between 1108 and 1113) or men (between 1116 and 1130) aged 40-79 yr. The -634C-->G polymorphism of the IL-6 gene and the 298C-->T polymorphism of the osteocalcin gene were associated with BMD in postmenopausal women, with the respective GG and TT genotypes representing risk factors for reduced bone mass. IL-6 and osteocalcin genotypes showed additive effects on BMD for postmenopausal women. The 2C-->T polymorphism of the VDR gene was associated with BMD in men, with the CT genotype contributing to reduced BMD. These results suggest that the IL-6 and osteocalcin genes are susceptibility loci for reduced BMD in postmenopausal women and that the VDR gene constitutes such a locus in men. The combined IL-6 and osteocalcin genotypes may prove informative for the assessment of osteoporosis in women.

Potential role of vitamin D receptor gene polymorphism in determining bone phenotype in young male athletes

The genetic difference among individuals partly explains variance in adaptive response to exercise through gene-environment interaction. The aim of this cross-sectional study was to evaluate the role of the vitamin D receptor (VDR) gene polymorphism, which locates at the translation initiation site, in the adaptations of bone to long-term impact loading. The VDR genotypes, as detected by endonuclease Fok I, and bone phenotypes of the lumbar spine and femoral neck were examined in 44 highly trained young male athletes and 44 age-matched nonathletic controls. As a whole, the athletes had a significantly higher bone mineral content resulting from a combination of increased volume and density at both sites than the controls. When the athletes were compared with the controls within each VDR genotype, however, the increased spinal volume was found only in the athletes with the FF but not in those with the Ff genotype("F" for the absence of the endonuclease Fok I restriction site and "f" for its presence). Differences in bone mineral content in the lumbar spine and femoral neck between the controls and the athletes were greater in subjects with FF than those with Ff. Our results suggest a gene-environment interaction in that the bone phenotypes in individuals with FF adapt to impact loading by producing stronger bone structure than those with the Ff do.

Biomarkers of bone health appropriate for evaluating functional foods designed to reduce risk of osteoporosis

Osteoporosis is a growing global problem. The health care costs and decreased productivity and quality of life are staggering. Much research is invested in life-style approaches to build peak bone mass during growth to prevent osteoporosis as well as to treat the disease in later life. Functional foods have enjoyed a niche in bone health. Foods fortified with Ca are most popular. Other bone nutrients such as vitamin D, Mg and vitamin K are sometimes added. Future products are likely to include enhancers of Ca absorption such as inulin or whey proteins. Dietary factors that reduce urinary Ca loss (plant proteins) or suppress bone resorption (possibly phyto-oestrogens) are also gaining attention. Methodologies for evaluating the effectiveness of functional foods on bone health include measures of bone quality such as bone densitometry or measures of Ca metabolism, particularly absorption. Biochemical markers for bone turnover are less satisfactory for diet-related effects. Use of a rare isotope, 41Ca, and accelerator mass spectrometry offers a new approach for assessing the ability of functional foods to suppress bone resorption.

Strategies for skeletal health in the elderly

Osteoporosis is a common disease in the elderly, and the fractures that result from this disorder affect 40 % of women and 14 % of men over the age of 50 years. The risk of fracture relates to bone mineral density and the risk of falling, among other factors. Low bone mineral density in the elderly can result from either low peak bone mass or accelerated bone loss, or a combination of the two. Nutritional factors play a role in both the attainment of peak bone mass and in the rate of age-related bone loss. The main determinants of peak bone mass are genetic factors, early-life nutrition, diet and exercise. Of the nutritional factors Ca, and particularly milk, are the most important contributors to peak bone mass. Some of these factors may interact; for example, a low dietary Ca in addition to an unfavourable vitamin D receptor gene polymorphism may result in low peak bone mass. The age-related changes in bone mass may also have a genetic basis, but deficiency of oestrogen is a major contributor. In addition, undernutrition is common in the elderly, and lack of dietary protein contributes both to impaired bone mineral conservation and increased propensity to fall. There is a decreased ability of the intestine to adapt to a low-Ca diet with increasing age. Other dietary factors include vitamin K, Zn and fruit and vegetables. Adequate nutritional status, particularly of Ca and vitamin D, is essential for the successful pharmaceutical treatment of osteoporosis. Thus, strategies for enhancing skeletal health in the elderly must begin in early childhood, and continue throughout life.

Genetics of osteoporosis: role of steroid hormone receptor gene polymorphisms

Osteoporosis is a common skeletal disease characterized by low bone mass and microarchitectural deterioration of bone tissue with a consequent increase in bone fragility and susceptibility to fracture. In the past years, twin and family study have shown that this disease recognizes a strong genetic component and that genetic factors play an important role in regulating bone mineral density (BMD). While in few isolate conditions osteoporosis can be inherited in a simple Mendelian pattern, due to single gene mutations, in the majority of cases has to be considered a multifactorial polygenic disease in which genetic determinants are modulated by hormonal, environmental and nutritional factors. Given the important role that steroid hormones play in bone cell development and in the maintenance of normal bone architecture, polymorphisms at receptor of the steroid/thyroid hormone receptor superfamily, such as estrogen receptor alpha (ERalpha) and Vitamin D receptor (VDR) have been thoroughly investigated in the last years and appeared to represent important candidate genes. The individual contribution of these genetic polymorphisms to the pathogenesis of osteoporosis remains to be universally confirmed and an important aim in future work will be to define their functional molecular consequences and how these polymorphisms interact with each other and with the environment to cause the osteoporotic phenotype. A further promising application of genetic studies in osteoporosis comes from their pharmacogenomic implications, with the possibility to give a better guidance for therapeutic agents commonly used to treat this invalidating disorder or to identify target molecules for new therapeutic agents.

Genetic association of vitamin D receptor polymorphisms with primary biliary cirrhosis and autoimmune hepatitis

Autoimmune hepatitis (AIH) and primary biliary cirrhosis (PBC) are immune-mediated chronic inflammatory diseases of the liver of unknown etiology. Genetic factors appear to be involved in the pathogenesis of both diseases. 1,25-Dihydroxyvitamin D(3) has been implicated as an immunomodulator, which acts through its own receptor (VDR). Polymorphisms of the VDR have been linked to a variety of autoimmune diseases. In this study VDR polymorphisms were analyzed in 123 patients with AIH, 74 patients with PBC, and 214 controls. VDR polymorphisms were assessed by BsmI, TaqI, ApaI, and Fok endonuclease digestion after specific polymerase chain reaction (PCR) amplification. We found a significant association between the BsmI polymorphisms in PBC patients in comparison with controls (chi(2) = 9.49, P =.009). Furthermore we detected a significant association of the Fok polymorphims in AIH patients in comparison to controls (chi(2) = 9.71, P =.008) indicating a genetic link of VDR polymorphisms to autoimmune liver diseases such as PBC and AIH in German patients. These findings contribute to the knowledge of the complex events determining immunologic tolerance in the liver. Further studies are needed to elucidate the mechanisms by which the vitamin D receptor contributes to the development of autoimmune diseases.

Cellular mechanisms of calcium and vitamin D in the inhibition of colorectal carcinogenesis

Convincing evidence is available showing that dietary calcium and vitamin D impede the development of colonic carcinogenesis. The major cellular modes of action of calcium and vitamin D which can contribute to the inhibition of colonic neoplasia are reviewed in this article. These consist of complex series of signaling events induced by the chemopreventive agents acting at various tiers of colonic cell organization.

Association of a T262C transition in exon 1 of estrogen-receptor-alpha gene with skeletal responsiveness to estrogen in post-menopausal women

Polymorphic genetic markers of estrogen-receptor-alpha (ERalpha) gene studied so far in osteoporosis reside in non-coding region with uncertain functional significance. The purpose of the present study was to search for nucleotides changes in the exon 1 and 5' regulatory region of ERalpha gene, to study the nature of their linkages to the previously reported Pvull polymorphism in intron 1 and their functional significance in postmenopausal osteoporosis. Direct sequencing of exon 1 and promotor region of ERalpha gene revealed a synonymous nucleotide substitution from T to C at position 262, 29 nucleotides downstream from the putative start codon. No nucleotide change was found in the promotor region. Linkage disequilibrium between the T262C polymorphism and the Pvull polymorphism in intron 1 of ERalpha gene was demonstrated in 129 post-menopausal women (p<0.001). After treating 96 post-menopausal with 0.3 mg or 0.625 mg conjugated equine estrogen (CEE) for 2 yr, vertebral bone mineral density (BMD) increased regardless of the T262C genotype. However, with regard to femoral neck BMD, only those subjects that were homozygous for the T262C polymorphism had an increase in femoral BMD (+5.9+/-1.4%, mean+/-SE; p<0.0001). Using analysis of covariance to assess the effects of the T262C polymorphism, the intronic Pvull polymorphism, doses of CEE and the corresponding baseline BMD on the changes in vertebral or femoral BMD after treatments, it was found that the change in vertebral BMD was related only to the baseline BMD (p<0.05). The change in femoral BMD was independently related to the T262C polymorphism (p<0.01) and the baseline femoral BMD (p<0.01). No effect of the Pvull polymorphism or the doses of CEE on femoral BMD was demonstrated. We concluded that the previously described intronic Pvull polymorphism of ERalpha gene is in linkage disequilibrium with a T262C polymorphism in exon 1. This T262C polymorphism appears to be more directly related to the skeletal response after long-term treatment with estrogen.

Lifestyle risk factors for osteoporosis in Asian and Caucasian girls

PURPOSE

We investigated ethnic differences in areal bone mineral density (aBMD; g x cm(-2)) and its determinants at two levels of maturity in Asian- and Caucasian-Canadian girls.

METHODS

Participants were 131 Asian (26 Tanner breast stage I (aTI) and 30 Tanner II (aTII)), and Caucasian (30 Tanner I (cTI) and 45 Tanner II (cTII)) girls. We measured calcium intake by a food frequency questionnaire, general physical activity, and extracurricular sports with a modified Physical Activity Questionnaire for Children and loaded physical activity by 7-d recall. Fat mass, lean mass, and aBMD for the total body (TB), and aBMD at the lumbar spine (LS), proximal femur (PF), femoral neck (FN), and trochanter (TR) were measured by DXA (Hologic QDR 4500). We used ANCOVA (controlling for size and lean and fat mass) to compare bone mineral content (BMC) and aBMD between ethnicities within Tanner stages.

RESULTS

Calcium intake was significantly lower for Asian girls in both TI and TII (P < 0.001) as compared with Caucasians. For physical activity measures, only the general score was greater in cTI than aTI (P < 0.05). Participation in loaded physical activities and extracurricular sports was significantly less for aTII than cTII (both, P < 0.01), whereas general physical activity did not differ. aBMD measures were similar between aTI and cTI. However, TB, PF, FN, and aBMD were significantly lower (approximately 9-14%) in aTII as compared with cTII.

CONCLUSION

Thus, there was greater ethnic disparity in lifestyle factors related to bone health and absolute measures of bone mineral with advanced maturity.

The polymorphism in the caudal-related homeodomain protein Cdx-2 binding element in the human vitamin D receptor gene

The major physiological activity of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] is the regulation of calcium absorption in the small intestine, and the level of vitamin D receptor (VDR) is an important factor in this regulation. In a previous study, we indicated-that the caudal-related homeodomain Cdx-2 played an important role in the intestine-specific transcription of the human VDR gene. In this study, the polymorphism was identified in the core sequence 5'-ATAAAAACTTAT-3' in the Cdx-2 binding site in the VDR gene promoter. In 261 Japanese women with genotyped VDR polymorphisms, 48 were genotype Cdx-A (adenine at -3731 nucleotides [nt] relative to the transcription start site of human VDR gene 5-ATAAAAACTTAT), 82 were genotype Cdx-G (guanine at -3731 nt, 5'-GTAAAAACTTAT-3'), and 131 were genotype Cdx-A/G (heterozygote). In postmenopausal Japanese women, the bone mineral density (BMD) in the lumbar spine (L2-L4) with the Cdx-G homozygote was 12% lower than that with the Cdx-A homozygote (p < 0.05). In electrophoretic gel mobility shift assay (EMSA), the oligonucleotide with Cdx-G allele markedly decreased the binding to Cdx-2 compared with that in the Cdx-A allele. The transcriptional activity of the VDR promoter with Cdx-G allele was decreased to 70% of the Cdx-A allele. In addition, in the herpes simplex virus thymidine kinase promoter, the Cdx-2 binding element with the G allele showed significantly lower transcriptional activity than that of the A allele. Thus, the polymorphism in the Cdx-2 binding site of the VDR gene (Cdx-polymorphism) would affect the expression of VDR in the small intestine. In addition, this polymorphism may modulate BMD in postmenopausal Japanese women.

An assessment of genetic markers as predictors of bone turnover in healthy adults

In 1992 a significant relationship between bone turnover and the vitamin D receptor (VDR) genotype was reported in Australian subjects of UK-Irish decent. Since then, several groups have investigated the relationship between VDR and other bone-related genotypes, bone mass and bone turnover in several populations. However, the results of these studies are conflicting. Therefore, our aim was to determine bone-related genotypes in a population of healthy Irish adults and relate these genotypes to the rate of bone turnover. One hundred and eighteen healthy Irish adults (aged 19-67 yr) were recruited and fasting blood and first void urines were collected from each subject. Bone-related genotype frequencies in healthy Irish adults were similar to those reported in other Caucasian populations and were in Hardy-Weinberg equilibrium. Estrogen receptor (Pvu II or Xba I), apolipoprotein E and collagen IA1 genotypes were not related to bone turnover. The tt VDR genotype was associated with significantly higher serum osteocalcin (29% and 40%) compared with the Tt and TT genotypes, respectively. The ff VDR genotype was associated with significantly higher urinary pyridinoline (by approximately 44% and approximately 29%) and deoxypyridinoline (by approximately 76% and approximately 58%) levels and higher serum osteocalcin (by approximately 25% and approximately 53%) compared with the Ff or FF genotypes, respectively. These findings suggest that healthy Irish adults with either the tt or ff VDR genotype have higher rates of bone turnover than those with Tt or TT, or Ff or FF genotypes, respectively, and therefore may have a higher risk of low bone mineral density and osteoporosis in later life.